Medical elastic stockings are stockings which exert pressure as measured at the ankle lying in the range 10 millimeters of mercury (mmHg) to more than 36 mmHg (equivalent to 13 hecto pascals (hPa) to 48 hPa, but the present description nevertheless uses mmHg as the unit of pressure measurement, given that it is universally used in the field of phlebology and medical compression). According to the French standard, such stockings are subdivided into four compression classes, namely class I (10 mmHg to 15 mmHg at the ankle); class II (15 mmHg to 20 mmHg); class III (20 mmHg to 36 mmHg); and class IV (>36 mmHg).
In order to enable the lower limbs to be compressed strongly, such elastic stockings are made of an elastic material, typically a knit of very tight texture and also incorporating an elastic weft yarn (generally a covered elastane). They are dimensioned as a function of the patient's leg, so as to obtain, by elasticity, the looked-for pressure profile and degree of compression.
The starting point of the invention is the observation that numerous users of such elastic stockings complain of discomfit in the instep, and of significant cooling of the foot after wearing the stocking for a few hours. This phenomenon is due to the very tight texture of the elastic stocking, which is needed in order to produce a medical effect on the leg, but which leads to residual compression on the foot, in particular in the malleolar and instep regions, where said residual compression produces excess pressure leading to the above-mentioned drawbacks. These drawbacks do not appear with support stockings and fashion stockings since they exert much less pressure.
This phenomenon is particularly marked with elastic stockings that deliver a degressive pressure profile so that they exert their highest pressure at the ankle, i.e. in the vicinity of the foot joint, i.e. where medically speaking there is no need to exert much pressure (the term “foot” is used to mean the entire region of the lower limb going from the malleolar region—the bony crests of the tibia and the fibula—to the ends of the toes, with the “instep” being defined as the front top portion situated over the arch of the foot).
Applying compression to the foot presents no advantage that has been demonstrated, which is hardly surprising, insofar as:                the anatomy of the arch of the foot lends itself poorly to compression, and any veins that might need compressing (in the sole) are under the arch. As a consequence of Laplace's equation, compression is very likely firstly to be vulnerable at the instep and the medial and external sides of the soles (1st and 5th radius) before possibly becoming effective at least to a small extent on the venous network of the sole (“Lejars' sole”). To be effective, it would be necessary to use an orthosis molded to have the shape of the arch of the foot (or to expect effectiveness only with subjects having grade 3 flat feet);        in the prone position, the natural position of the foot is favorable to venous drainage of the front of the foot, whereas while standing the flattening of the sole doubtless has an effect in terms of compression that is better than anything that could be achieved by a highly compressive elastic stocking on the foot. The only vulnerable position is the sitting position associated with total inactivity of the foot and of the ankle.        
In addition, there exist minor limits, or clear reserves, on applying compression to the foot:                with some subjects, the arterial vascularization of the front of the foot is vulnerable specifically as a result of anatomy. Normally, this vascularization benefits from anastomosis between the network of the dorsal artery of the foot (anterior terminal branch of the tibial artery which runs along the instep and the back of the foot prior to going down between the metatarsal bones) and the medial plantar artery (posterior branch of the tibial artery which runs along the medial edge of the arch of the foot). Sometimes such anastomosis does not exist, and as a result arterial vascularization of the toes is made fragile. This is doubtless responsible for the feeling of cold feet in certain patients;        in other patients, problems arise because of deformations of the metatarsus (hallux valgus, overlapping little toe, sag foot), still by the combination of “Laplace's equation+compression becoming excessive on a surface having a small radius of curvature”;        above all, in the event of severe arterial insufficiency (pressure index at the ankle <0.50), very distal arterial disease, vulnerable skin (diabetes with advanced microangiopathy, patients being treated over long term with corticotherapy, very aged subjects with cutaneous atrophy, . . . ), the iatrogenic risk of excess pressure on the instep and the back of the foot becomes highly perceptible. Under such circumstances, elasticated compression can be the result only of specialized advice.        
In all, the only advantage in applying compression to the foot lies in:                preventing edema and venous congestion in the instep due to too sudden a change in pressure going from the foot to the ankle (where the highest pressure is exerted); and        to keep the stocking properly in place.        
In addition, pressure at the foot is not controlled and consequently pressure at the instep can be even greater than the pressure exerted at the ankle.